Lightweight steel door for vehicle and method for manufacturing the same

ABSTRACT

A vehicle door assembly comprises an inner panel integrally formed by upper and lower horizontal beams interconnected by front and rear upright beams, and an outer panel bonded to the inner panel. The frame portion comprises opposite front and rear U-shaped side frame members non-detachably attached to each other by upper and lower intermediate frame members so as to form a continuous perimeter. The side frame members are made of a first steel material and the intermediate frame members made of a second steel material, which is different from the first steel material. A method for manufacturing the inner panel comprises the steps: providing U-shaped sheets of the first steel material, providing top and bottom sheets of the second steel material, non-detachably connecting the U-shaped sheets to the top and bottom sheets so as to form a blank, and stamping the blank into the frame portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application No. 13/362,479 filedOct. 1, 2012, now U.S. Pat. No. 8,910,999, which claims the benefit ofU.S. Provisional Application Ser. No. 61/541,568 filed Sep. 30, 2011,the disclosures of which are incorporated herein by reference and towhich priority is claimed.

FIELD OF THE INVENTION

The present invention relates to vehicle door assemblies and methods formanufacturing thereof in general and, more particularly, to alightweight vehicle door assembly and method for manufacturing the sameusing components made of various interconnected high strength steelgrades.

BACKGROUND OF THE INVENTION

Conventionally, vehicle doors comprise a supportive inner panel made ofsteel material. An outer panel is attached to the inner panel. Theconventional inner panel is deep-drawn from mild steel. A beltline beambeneath the window is welded to the inner panel and can be placed eitherinwardly of or outwardly of the window. Typically, the vehicle doorsinclude a generally horizontally extending side impact guard beam madeof steel that has a considerably higher mechanical strength than thesteel from which the inner panel is made. The impact guard beam iswelded to the inner panel and placed nearest the outer panel. Arelatively flat trim is fastened to the inner panel. The inner doorcomponents, such as locks, window guides and window elevators, aremounted to the inner panel.

Furthermore, steel sheet has been the most widely used raw material formotor vehicle doors. Steel doors are inexpensive and simple tomanufacture. However, conventional steel door designs are relativelyheavy in comparison to the mass of newly designed aluminum doors.Accordingly, there is a tendency in the automotive industry to replacesteel doors with the doors made of aluminum. The aluminum doors,although lighter than conventional steel doors, are however costlierthan steel doors and more complex, difficult and expensive tomanufacture.

Therefore, vehicle doors made of steel are susceptible to improvementsthat may enhance their performance, cost and weight. With this in mind,a need exists to develop an improved vehicle door made of high-strengthsteel with reduced weight comparable to that of the weight of aluminumdoors, improved performance, and inexpensive to manufacture.

SUMMARY OF THE INVENTION

The present invention is directed to a novel lightweight vehicle doorassembly, and a method for manufacturing the same.

The vehicle door assembly according to the present invention comprisesan inner panel in the form of a substantially rectangular frame portionhaving a continuous perimeter integrally formed by upper and lowerhorizontal beams interconnected by front and rear upright beams, and anouter panel attached to the inner panel. The frame portion comprisesopposite front and rear U-shaped side frame members non-detachablyattached to each other by upper and lower intermediate frame members soas to form a continuous perimeter. The side frame members are made of afirst steel material and the intermediate frame members made of a secondsteel material. The first steel material of the side frame members isdifferent than the second steel material of the intermediate framemembers.

The method for manufacturing an inner panel of a vehicle door assemblyaccording to the present invention comprises the steps of providingfront and rear flat U-shaped steel sheets of a first steel material suchthat each of the front and rear U-shaped steel sheets comprises a crossportion and a pair of spaced apart leg portions extending from the crossportion, providing top and bottom flat steel sheets of a second steelmaterial, non-detachably connecting each of the leg portions of each ofthe U-shaped steel sheets to a respective one of the top and bottomsteel sheets so as to form a flat door perimeter frame blank, andstamping the door perimeter frame blank into a perimeter frame portionof an inner panel. The first steel material of the front and rear flatU-shaped steel sheets is different than the second steel material of thetop and bottom flat steel sheets. Moreover, the frame portion comprisesopposite front and rear U-shaped side frame members non-detachablyattached to each other by upper and lower intermediate frame members soas to form the continuous perimeter. The side frame members are made ofthe first steel material and the intermediate frame members are made ofthe second steel material, which is higher in strength and thickness toimprove resistance to side intrusion.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthe specification. The drawings, together with the general descriptiongiven above and the detailed description of the exemplary embodimentsand methods given below, serve to explain the principles of theinvention. In such drawings:

FIG. 1 is a side view of a vehicle right-side front door assemblyaccording to an exemplary embodiment of the present invention;

FIG. 2A is a partial perspective view of the vehicle right-side frontdoor assembly according to the exemplary embodiment of the presentinvention;

FIG. 2B is a partial perspective view of the vehicle right-side frontdoor assembly according to an alternative embodiment of the presentinvention;

FIG. 3 is a sectional view of the vehicle right-side front door assemblyaccording to the exemplary embodiment of the present invention;

FIG. 4 is an exploded assembly drawing in perspective of the vehicleright-side front door assembly according to the exemplary embodiment ofthe present invention;

FIG. 5 is an exploded assembly drawing in perspective of structuralelements of the vehicle right-side front door assembly according to theexemplary embodiment of the present invention;

FIG. 6 is a perspective view of an inner panel of the vehicle right-sidefront door assembly according to the exemplary embodiment of the presentinvention;

FIG. 7 is a side view of the inner panel of FIG. 6;

FIG. 8 is top view of the inner panel of FIG. 6;

FIG. 9A is a side view of a multi-piece laser welded blank for stampinga frame portion of the inner panel according to the exemplary embodimentof the present invention;

FIG. 9B is a side view of the frame portion of the inner panel accordingto the exemplary embodiment of the present invention stamped from themulti-piece laser welded blank shown in FIG. 9A;

FIG. 10 is a side view of the inner panel of according to the exemplaryembodiment of the present invention showing cross-sectional lines;

FIG. 11 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 1-1 shown in FIG. 10;

FIG. 12 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 2-2 shown in FIG. 10;

FIG. 13 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 3-3 shown in FIG. 10;

FIG. 14 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 4-4 shown in FIG. 10;

FIG. 15 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 5-5 shown in FIG. 10;

FIG. 16 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 6-6 shown in FIG. 10;

FIG. 17 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 7-7 shown in FIG. 10; and

FIG. 18 is a cross-sectional view of the inner panel of FIG. 6 takenalong the line 8-8 shown in FIG. 10.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S) AND EXEMPLARY METHOD(S)

Reference will now be made in detail to exemplary embodiments andmethods of the invention as illustrated in the accompanying drawings, inwhich like reference characters designate like or corresponding partsthroughout the drawings. It should be noted, however, that the inventionin its broader aspects is not limited to the specific details,representative devices and methods, and illustrative examples shown anddescribed in connection with the exemplary embodiments and methods.

This description of exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description, relativeterms such as “horizontal,” “vertical,” “front,” “rear,” “upper”,“lower”, “top” and “bottom” as well as derivatives thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) should be construed torefer to the orientation as then described or as shown in the drawingfigure under discussion and to the orientation relative to a vehiclebody. These relative terms are for convenience of description andnormally are not intended to require a particular orientation. Termsconcerning attachments, coupling and the like, such as “connected” and“interconnected,” refer to a relationship wherein structures are securedor attached to one another either directly or indirectly throughintervening structures, as well as both movable or rigid attachments orrelationships, unless expressly described otherwise. The term“operatively connected” is such an attachment, coupling or connectionthat allows the pertinent structures to operate as intended by virtue ofthat relationship. Additionally, the word “a” as used in the claimsmeans “at least one”.

FIGS. 1, 2A, 3, 4 and 5 illustrate a right-side front door assembly 10of a motor vehicle (especially, a midsize car) according to an exemplaryembodiment of the present invention. The door assembly 10 comprises aninner panel 12, an outer panel 14 attached to and supported by flangesof the inner panel 12, a module extension 16 used to receive apre-assembled door module unit, attached to and supported by an innersurface (i.e., facing a passenger compartment of the motor vehicle) ofthe inner panel 12, an inner beltline element (or beam) 15 (shown inFIGS. 4 and 5) disposed between the inner panel 12 and the moduleextension 16, a hinge reinforcement member 18 fastened to a front end 12_(F) of the inner panel 12, a window frame 20 for a window pane 21retractably movable in and out of a cavity 11 formed inside the doorassembly 10 between the inner panel 12 and the module extension 16 (asshown in FIG. 3), and a front window guide 26.

The inner panel 12, according to the exemplary embodiment of the presentinvention shown in detail in FIGS. 4-8, is three-piece stampedsubassembly including a substantially rectangular perimeter frameportion 28 having a continuous perimeter, a single intermediate upright(vertical) beam (structural element) 38 and a single forward-transverse(or gusset) beam (structural element) 40 that both are non-detachablysecured to the perimeter frame portion 28 to stiffen the inner panel 12,provide side intrusion protection, and support the thin-gauge outerpanel 14 to improve its stiffness and oil canning performance. Each ofthe intermediate upright beam 38 and the gusset beam 40 has an open,hat-shaped profile and is formed separately from the perimeter frameportion 28. The perimeter frame portion 28, the intermediate uprightbeam 38 and the gusset beam 40 are then non-detachably secured to eachother, such as by welding, and preferably by laser welding to form theinner panel 12. The perimeter frame portion 28 of the inner panel 12 isintegrally formed by upper and lower horizontal beams 30 and 32,respectively, interconnected by front and rear upright beams 34 and 36,respectively.

As illustrated in detail in FIGS. 6 and 7, the intermediate upright beam38 substantially vertically extends between the upper and lowerhorizontal beams 30 and 32 through approximately the middle of the frameportion 28 of the inner panel 12, while the forward-transverse beam 40is angled so as to extend between the upper horizontal beam 30 and thefront upright beam 34. The gusset beam 40 acts as a brace between thefront upright beam 34 (and the hinge reinforcement member 18) and theupper horizontal beam 30 beneath the window frame 20. This reinforcesthe door assembly 10 to improve stiffness. Alternatively, the innerpanel 12 may include only the single intermediate upright beam 38, butnot the gusset beam 40. The upright vertical beam 38 together with theinner panel 12 and the gusset beam 40 provide an effective means toresist side impact intrusions. Thus, according to the exemplaryembodiment of the present invention, the inner panel 12 of the doorassembly 10 is devoid of the conventional horizontal intrusion beam (orside impact guard beam) extending substantially horizontally between thefront and rear upright beams (structural elements) 34 and 36. Thebeltline beams (i.e., the upper horizontal beam 30 and the innerbeltline beam 15) provide stiffness.

The inner panel 12 of the door assembly 10 is manufactured from AdvancedHigh Strength Steels (AHSS). The method of manufacturing the inner panel12 of the door assembly 10 according to the exemplary embodiment of thepresent invention is described below. First, as best shown in FIG. 9A, asubstantially rectangular, flat, single door perimeter frame blank 50having a continuous perimeter is integrally formed from four pieces ofsteel sheet in order to manufacture the multi-piece frame portion 28 ofthe inner panel 12. The pieces of steel sheet includes two oppositesheets of front and rear flat U-shaped steel sheets 52 _(F) and 52 _(R),respectively, of a first advanced high strength steel material, and twoopposite substantially rectangular top and bottom flat steel sheets 54_(T) and 54 _(B), respectively, of a second advanced high-strength steelmaterial, which is different from the first steel material and is ofhigher strength and thickness to improve resistance to side intrusion.

Subsequently, the single laser welded blank 50 is stamped into theperimeter frame portion 28 of the inner panel 12 either by hot stampingor cold stamping.

According to the exemplary embodiment of the present invention, in caseof cold-stamping the perimeter frame blank 50, the first steel materialis a grade DP 780 steel having thickness (or gauge) of 0.60 mm, whilethe second steel material is grade MS 1300 martensitic steel havingthickness of 1.00 mm. It should be understood that steel material ischaracterized by grade (thus, strength) and thickness (or gauge). Forexample, a TRIP steel grade can be used instead of the grade DP 780high-strength steel if there is a need for increased formability in theperimeter frame blank 50. Moreover, the particular grades of the firstand second steel materials used in case of hot-stamping the perimeterframe blank 50 are different from those used when cold-stamping.However, in any case, the second steel material is different from thefirst steel material and is of higher strength and thickness.

Each of the front and rear U-shaped steel sheets 52 _(F), 52 _(R)comprises a cross portion 52 _(FC), 52 _(RC) and a pair of spaced apartleg portions 52 _(F1) and 52 _(F2), 52 _(R1) and 52 _(R2) extending fromthe cross portion 52 _(FC), 52 _(RC). In order to form the steel blank50, the front and rear flat U-shaped steel sheets 52 _(F) and 52 _(R)are oriented so that the leg portions 52 _(F1), 52 _(F2) and 52 _(R1),52 _(R2) are aligned and face each other. Then, the top and bottom steelsheets 54 _(T) and 54 _(B) are placed between the leg portions 52 _(F1)and 52 _(F2), 52 _(R1) and 52 _(R2) of the U-shaped steel sheets 52_(F), 52 _(R) so as to be aligned therewith. Subsequently, each of theleg portions 52 _(F1) and 52 _(F2), 52 _(R1) and 52 _(R2) of each of theU-shaped steel sheets 52 _(F), 52 _(R) is non-detachably connected(i.e., fixed) at a free end thereof to the respective top and bottomsteel sheets 54 _(T) and 54 _(B) by any appropriate means known in theart so as to form the steel blank 50. According to the exemplaryembodiment of the present invention, the U-shaped steel sheets 52 _(F),52 _(R) are seam-welded to the top and bottom steel sheets 54 _(T) and54 _(B), such as by laser welding, thus forming a single laser weldedblank 50. As a result, the single blank 50 contains different steelmaterials, i.e., different grades and/or gauges of advanced highstrength steel. Specifically, the leg portions 52 _(F1) and 52 _(R1) ofthe front and rear flat U-shaped steel sheets 52 _(F) and 52 _(R),respectively, are seam-welded to distal ends of the top steel sheet 54_(T) through laser weld joints 53 ₁ and 53 ₃, while the leg portions 52_(F2) and 52 _(R2) of the front and rear flat U-shaped steel sheets 52_(F) and 52 _(R), respectively, are seam-welded to distal ends of thebottom steel sheet 54 _(B) through laser weld joints 53 ₂ and 53 ₄.

Subsequently, the single laser welded blank 50 is stamped into theperimeter frame portion 28 of the inner panel 12 either by hot stampingor cold stamping. In case of hot stamping, the flat steel blank 50 isfirst heated, then put into a forming tool to form the required shape ofthe frame portion 28, then the hot-stamped frame portion 28 remains inthe tool as it is quickly cooled to increase its strength.

The stamped frame portion 28 of the inner panel 12, illustrated indetail in FIG. 9B, includes front and rear opposite U-shaped side framemembers 28 ₁ and 28 ₂ (stamped from the front and rear flat U-shapedsteel sheets 52 _(F) and 52 _(R)) non-detachably secured to each otherby upper and lower intermediate frame members 28 ₃ and 28 ₄ (stampedfrom the top and bottom steel sheets 54 _(T) and 54 _(B)), spaced fromeach other, so as to form the continuous perimeter. Moreover, accordingto the exemplary embodiment of the present invention, leg portions ofthe front and rear side frame members 28 ₁ and 28 ₂ are seam-welded todistal ends of the upper and lower intermediate frame members 28 ₃ and28 ₄ through laser weld joints 53 ₁, 53 ₂, 53 ₃ and 53 ₄. Thus, theframe portion 28 of the inner panel 12 is integrally formed by the frontand rear U-shaped side frame members 28 ₁ and 28 ₂ interconnected by theupper and lower intermediate frame members 28 ₃ and 28 ₄.

Furthermore, as noted above, in case of cold-stamping the perimeterframe blank 50, the side frame members 28 ₁ and 28 ₂ of the frameportion 28 are made of the DP 780 grade steel having a thickness of 0.60mm, while the upper and lower intermediate frame members 28 ₃ and 28 ₄are made of MS1300 grade martensitic steel having a thickness of 1.00mm. Thus, the steel material of the side frame members 28 ₁ and 28 ₂ isdifferent from the steel materials of the upper and lower intermediateframe members 28 ₃ and 28 ₄ (i.e., has different grade and/or gauge).

Next, each of the intermediate upright beam 38 and the gusset beam 40 ishot- or cold-stamped separately from the frame portion 28 and from eachother. In other words, each of the intermediate upright beam 38 and thegusset beam 40 according to the exemplary embodiment of the presentinvention is a single-piece hot or cold stamped member. The intermediateupright beam 38 is stamped from a flat, very thin gauge sheet of highstrength steel blank of a third steel material, such as USIBOR® 1500Phaving a thickness of 0.60 mm, that is different from the first steelmaterial of the side frame members 28 ₁ and 28 ₂ and the second steelmaterial of the intermediate frame members 28 ₃ and 28 ₄. Similarly, thegusset beam 40 is stamped from a flat, very thin gauge sheet of highstrength steel blank of a third steel material, such as USIBOR® 1500Phaving a thickness of 0.60 mm, that is different from the first steelmaterial of the side frame members 28 ₁ and 28 ₂ and the second steelmaterial of the intermediate frame members 28 ₃ and 28 ₄.

Currently, minimum thicknesses of hot stamped steel parts are about 0.90mm. USIBOR® 1500P is a hardenable boron alloyed steel coated with anAl—Si coating from ArcelorMittal, frequently used when high strength isrequired. Aluminum-silicon coatings protect steel from oxidation duringheating and provide corrosion protection for the component. In case ofhot-stamping process, manufacturing is done in a press hardening line,where a heated (900° C.) steel blank is formed and then rapidly cooled(quenched) to room temperature in a water-cooled forming tool. Theresult is a hardened part with a yield strength of about 1100 MPa and anultimate strength of about 1500 MPa.

Finally, the frame portion 28, the intermediate upright beam 38 and thegusset beam 40 are non-detachably joined together after stamping (suchas welded, and preferably laser welded) to form the multi-part innerpanel 12 as shown in FIGS. 6-8.

As best shown in FIGS. 6 and 7, the intermediate upright beam 38substantially vertically extends between the upper and lower horizontalbeams 30 and 32 through approximately the middle of the perimeter frameportion 28 of the inner panel 12 such that distal ends of theintermediate upright beam 38 are non-detachably attached to the upperand lower intermediate frame members 28 ₃ and 28 ₄ of the perimeterframe portion 28. Thus, the intermediate upright beam 38 extends betweenthe thicker sections of the frame portion 28. In turn, the gusset beam40 extends between the upper horizontal beam 30 and the front uprightbeam 34 such that distal ends of the gusset beam 40 are non-detachablyattached to the upper intermediate frame member 28 ₃ and the front sideframe member 28 ₁ of the frame portion 28.

As noted above, each of the intermediate upright beam 38 and the gussetbeam 40 is hot- or cold-stamped separately from the frame portion 28 andfrom each other. Alternatively, the inner panel 12 can be made in theform of a single-piece hot- or cold-stamped member.

As further illustrated in detail in FIGS. 6 and 7, the intermediateupright beam 38 and the gusset beam 40 define three openings 42, 44 and46 in the inner panel 12. The openings 42, 44 and 46 are formed withinthe rectangular frame portion 28 (defined by the horizontal beams 30, 32and the upright beams 34, 36) by the intermediate upright beam 38 andthe gusset beam 40. Specifically, the first opening 42 is definedbetween the upper and lower horizontal beams 30 and 32, the rear uprightbeam 36 and the intermediate upright beam 38. The second opening 44 isdefined between the gusset beam 40, the front upright beam 34, the lowerhorizontal beam 32 and the intermediate upright beam 38. The thirdopening 46 is defined between the upper horizontal beam 30, the gussetbeam 40 and the front upright beam 34. Alternatively, the gusset beam 40and the opening 46 need not be provided.

According to the exemplary embodiment of the present invention, as shownin FIGS. 10 and 12-16, each of the lower horizontal beam 32, the frontupright beam 34 and the rear upright beam 36 of the frame portion 28 hasan open, hat-shaped profile with a crown portion 33 c, 35 c and 37 c,respectively, and a pair of spaced apart flanges 33 _(F), 35 _(F) and 37_(F), respectively, extending from the crown portion in the directionaway from an interior (i.e., a passenger compartment) of the vehicle andtowards the outer panel 14 of the door assembly 10. Moreover, each ofthe flanges 33 _(F), 35 _(F) and 37 _(F) is provided with a lip 33 _(L),35 _(L) and 37 _(L), respectively, extending from a distal end thereof.Each of the lips 33 _(L), 35 _(L) and 37 _(L) is shaped and sized tomeet (engage) an inner surface of the outer panel 14.

As further illustrated in FIGS. 6-8, 10 and 18, the upper horizontalbeam 30 includes a main portion 31 _(M) and a flange 31 _(F) extendingfrom the main portion 31 _(M) in the direction away from the interior(i.e., the passenger compartment) of the vehicle and towards the outerpanel 14 of the door assembly 10. The flange 31 _(F) is provided with alip 31 _(L) extending from a distal end thereof. Each of the lips 31_(L) is shaped to meet (engage) an inner surface of the outer panel 14.The main portion 31 _(M) extends substantially vertically in thedirection of the crown portions 33 _(C), 35 _(C) and 37 _(C) of thelower horizontal beam 32, the front upright beam 34 and the rear uprightbeam 36 of the frame portion 28.

Further according to the exemplary embodiment of the present invention,as shown in FIGS. 10, 11 and 17, both the intermediate upright beam 38and the gusset beam 40 have an open, Hat-shaped profile each having acrown portion 39 _(C) and 41 _(C), respectively, and a pair of spacedapart flanges 39 _(F) and 41 _(F), respectively, extending from thecrown portion 39 _(C), 41 _(C) in the direction away from the interior(i.e., the passenger compartment) of the vehicle and towards the outerpanel 14 of the door assembly 10. Moreover, each of the flanges 39 _(F)and 41 _(F) is provided with a lip 39 _(L) and 41 _(L), respectively,extending from a distal end thereof. Each of the lips 39 _(L) and 41_(L) is shaped to meet (engage) an inner surface of the outer panel 14.

The front end 12 _(F) of the inner panel 12 is an end portion of theinner panel 12 at which the door assembly 10 is pivotally suspended to afront hinge pillar (A-pillar) of a body of the motor vehicle by at leastone hinge member through the hinge reinforcement member 18. Preferably,the inner panel 12 is pivotally suspended to the front hinge pillar(A-pillar) of the vehicle body by two hinges and has the integratedhinge reinforcement member 18 welded to the front end 12 _(F) of theinner panel 12. A rear end 12 _(R) of the inner panel 12 is an endportion of the inner panel 12 at which a lock of the door assembly 10 isprovided so as to cooperate with a mid-pillar (B-pillar) of the body ofthe motor vehicle. As noted above, the hinge reinforcement member 18 isfastened to the front end 12 _(F) of the inner panel 12. According tothe exemplary embodiment of the present invention, the hingereinforcement member 18 is formed from a laser welded blank of threeseparate pieces of high-strength steel sheet, as shown in FIG. 5,integrally fixed to each other, as shown in FIG. 4: a primary piece 18 ₁made of dual-phase steel such as DP 600 having thickness of 0.60 mm andtwo vertically spaced secondary pieces 18 ₂ each made of dual-phasesteel such as DP 980 having thickness of 1.50 mm. Each of the secondarypieces 18 ₂ of the hinge reinforcement member 18 can be provided withtwo washers 18 ₃ each made of dual-phase steel such as DP 600 havingthickness of 3.50 mm. Alternatively, the hinge reinforcement member 18can be made of other grades and gauges of steel. In other words, thehinge reinforcement member 18 is formed from the laser welded blankincluding the primary steel piece 18 ₁ and two secondary steel pieces 18₂ seam-welded together into the single laser welded blank, which is thenstamped into a final part (the hinge reinforcement member 18) includingdifferent grades (or types) and thickness of steel.

The outer panel 14 according to the exemplary embodiment of the presentinvention is adhesively bonded to the lips 31 _(L), 33 _(L), 35 _(L), 37_(L), 39 _(L) and 41 _(L) of the flanges 31 _(F), 33 _(F), 35 _(F), 37_(F), 39 _(F) and 41 _(F), respectively, of the inner panel 12, closingout the hat-shaped sections of the lower horizontal beam 32, the frontupright beam 34 and the rear upright beam 36 of the frame portion 28,and the intermediate upright and gusset beams 38 and 40 and forming aneven stronger, stiffer inner structure. As best shown, in FIGS. 4 and 5,beads 17 of an appropriate adhesive material are deposited between thelips 31 _(L), 33 _(L), 35 _(L), 37 _(L), 39 _(L) and 41 _(L) of theinner panel 12 and the outer panel 14. This enables the outer panel 14to stabilize the flanges 31 _(F), 33 _(F), 35 _(F), 37 _(F), 39 _(F) and41 _(F) of the inner panel 12 during side intrusion events, thusimproving the resistance of the door assembly 10 to side intrusion. Inthe exemplary embodiment of the present invention shown in FIG. 5, thebeads 17 of the adhesive material are deposited to an inner surface ofthe outer panel 14 so as to face the lips 31 _(L), 33 _(L), 35 _(L), 37_(L), 39 _(L) and 41 _(L) of the inner panel 12. Alternatively, thebeads 17 of the adhesive material are deposited directly to the lips 31_(L), 33 _(L), 35 _(L), 37 _(L), 39 _(L) and 41 _(L) of the inner panel12. Preferably, the adhesive material used to adhesively bond the outerpanel 14 to the inner panel 12 is a structural adhesive havingsufficient bond strength to adhere the inner and outer panels 12 and 14without causing a “read-through” effect on the outside of the outerpanel 14.

According to the exemplary embodiment of the present invention, theouter panel 14 is formed of steel sheet, such as exposed qualitydual-phase FF280DP steel of ArcelorMittal, having a thickness of about0.55 mm. The lightweight, thin-gauge high-strength steel outer panel 14reduces weight of the vehicle door relative to the conventional, lowerstrength, heavier gauge designs without compromising dent resistance.The lightweight outer panel 14 made from the 0.55 mm FF280DP gradehigh-strength steel maintains required dent resistance at minimum mass.The outer panel 14 structurally bonded to the inner panel 12 enables theouter panel 14 to work synergistically with the inner panel 12 toachieve performance requirements.

The module extension 16 according to the exemplary embodiment of thepresent invention is formed of dual-phase steel such as of DP500 gradehaving a thickness of about 0.50 mm, or other suitable grades and gaugesof steel. The inner beltline beam 15 is fixed between the upperhorizontal beam 30 of the inner panel 12 and the module extension 16 andis formed of hot-stamped high strength steel, such as USIBOR® 1500Phaving a thickness of about 0.50 mm, or other suitable grades and gaugesof steel. A beltline inner bracket 19 is made of DP500 steel gradehaving thickness of 0.55 mm in the exemplary embodiment of the presentinvention.

As further illustrated in FIGS. 4 and 5, the window frame 20 comprisesan outer window frame member 22 and an inner window frame member 24facing the passenger compartment of the vehicle. The outer and innerwindow frame members 22, 24 are welded to each other and to the innerpanel 12, preferably by laser or spot welding. The outer and innerwindow frame members 22 and 24 may be formed by cold- or hot-stampingfrom integral, multi-piece laser weld blanks, with laser weld jointsstaggered between the outer and inner window frame members 22, 24 of thewindow frame 20. Alternatively, the outer and inner window frame members22 and 24 may be roll-formed. The outer window frame member 22 accordingto the exemplary embodiment of the present invention, shown in detail inFIGS. 4 and 5, is made of three separate pieces 22 ₁, 22 ₂ and 22 ₃,which are integrally fixed to each other, such as by laser weldingthrough laser weld joints 23 ₁ and 23 ₂. The outer window frame member22 is manufactured by, first, providing first, second and third flatsheets made of first, second and third outer window steel materials,respectively, which are different from each other. Then, the first,second and third flat sheets are non-detachably attached to each otherso as to form a single outer window blank. Next, the outer window blankis stamped into the single outer window frame member 22.

According to the exemplary embodiment of the present invention, thefirst piece 22 ₁ of the outer window frame member 22 is made of BH210grade steel with thickness of 0.50 mm (first outer window steelmaterial), the second piece 22 ₂ is made of DP500 grade steel havingthickness of 0.55 mm (second outer window steel material), while thethird piece 22 ₃ (a mirror flag portion) is made of USIBOR® 1500P gradesteel having thickness of 0.50 mm (third outer window steel material).Alternatively, other suitable grades and gauges of steel can be used.

The inner window frame member 24 according to the exemplary embodimentof the present invention, shown in detail in FIGS. 4 and 5, is made oftwo separate pieces 24 ₁ and 24 ₂, which are integrally fixed to eachother, such as by laser welding through a laser weld joint 25. The innerwindow frame member 24 is manufactured by, first, providing first andsecond flat sheets made of first and second inner window steelmaterials, respectively. Next, the first and second flat sheets arenon-detachably attached to each other so as to form a single innerwindow blank. Then, the inner window blank is stamped into the singleinner window frame member. The first and second inner window steelmaterials are different from each other.

According to the exemplary embodiment of the present invention, thefirst piece 24 ₁ of the outer window frame member 22 is made of DP500grade steel having a thickness of 0.58 mm (first inner window steelmaterial), while the second piece 24 ₂ (including a mirror flag portion)is made of dual-phase DP 600 steel having a thickness of 0.76 mm (secondinner window steel material). Alternatively, other suitable grades andgauges of steel can be used.

The front window guide 26, normally an add-on component used only forglass fixation, is utilized in the present design as a structuralelement, providing stiffness to the mirror flag and stiffness to theupper window frame structure. Also, the front window guide 26 stiffensthe mirror flag area of the window frame 20. According to the exemplaryembodiment of the present invention, the front window guide 26 is madeof Drawing Quality Special Killed Steel DQSK having a thickness of 0.80mm (or other suitable grades and gauges of steel). A window guidebracket 27 is made of DP780 grade steel having thickness of 0.50 mm inthe exemplary embodiment of the present invention.

As illustrated in FIGS. 2A and 6-8, the rear upright beam 36 of theinner panel 12 is provided with a deep draw section 29 in contact withthe inner window frame member 24. Alternatively, as illustrated in FIG.2B, a deep draw section 29′ can be integrated into (i.e., formed as asingle piece with) the inner window frame member 24 of the window frame20 for better manufacturability and possibly better structuralperformance.

The present invention provides a novel lightweight steel door assemblyfor a vehicle by creating optimized load paths and by causing everycomponent in the door assembly to perform multiple strengthening andstiffening functions. The door assembly according to the presentinvention provides weight reduction in a steel solution that approachesthat of an aluminum solution, while maintaining required strength andstiffness, at a total manufacturing cost that is substantially lowerthan that of aluminum solutions. The present invention employs load pathoptimization to develop an efficient structure (i.e., places structuralelements along important load paths). This maximizes efficiency andbrings all components of the door assembly together to each performmultiple functions in achieving door structural strength, stiffness, andpassenger compartment intrusion protection performance goals. Thepresent invention further utilizes novel applications of materials, hotand/or cold stamping, and laser welding. The door assembly of thepresent invention includes an inner panel comprising a frame portion hotor cold stamped from a multi-piece laser welded blank, and separatelyhot or cold stamped intermediate upright and gusset beams non-detachablyconnected to the frame portion. The hot stamping design also providesstrength and stiffness in the beltline area, eliminating the need foradditional reinforcements in this area. The unique door architecture,with the reinforcing inner panel disposed outside of the glass windowpane and supported by the outer panel, provides improved stiffness andside intrusion behaviour.

The foregoing description of the exemplary embodiments of the presentinvention has been presented for the purpose of illustration inaccordance with the provisions of the Patent Statutes. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Obvious modifications or variations are possible in light ofthe above teachings. The embodiments disclosed hereinabove were chosenin order to best illustrate the principles of the present invention andits practical application to thereby enable those of ordinary skill inthe art to best utilize the invention in various embodiments and withvarious modifications as are suited to the particular use contemplated,as long as the principles described herein are followed. Thus, changescan be made in the above-described invention without departing from theintent and scope thereof. It is also intended that the scope of thepresent invention be defined by the claims appended thereto.

What is claimed is:
 1. A method for manufacturing a vehicle doorassembly comprising an inner panel in the form of a substantiallyrectangular perimeter frame portion having a continuous perimeterintegrally formed by upper and lower horizontal beams interconnected byfront and rear upright beams, said method comprising the steps of:providing front and rear flat U-shaped steel sheets of a first steelmaterial, each of said left and right U-shaped steel sheets comprising across portion and a pair of spaced apart leg portions extending fromsaid cross portion; providing top and bottom flat steel sheets of asecond steel material; non-detachably connecting each of said legportions of each of said U-shaped steel sheets to a respective one ofsaid top and bottom steel sheets so as to form a flat door perimeterframe blank; and stamping said door perimeter frame blank into saidperimeter frame portion of said inner panel; said first steel materialof said front and rear flat U-shaped steel sheets being different fromsaid second steel material of said top and bottom flat steel sheets;said frame portion comprising opposite front and rear U-shaped sideframe members non-detachably attached to each other by upper and lowerintermediate frame members so as to form said continuous perimeter; saidside frame members made of said first steel material and saidintermediate frame members made of said second steel material.
 2. Themethod for manufacturing said vehicle door assembly as defined in claim1, wherein said second steel material of said intermediate frame membersis thicker than said first steel material of said side frame members. 3.The method for manufacturing said vehicle door assembly as defined inclaim 1, further comprising the steps of: providing a flat sheet ofsteel blank of a third steel material that is different from said secondsteel material of said intermediate frame members; stamping said flatsheet of steel blank into a single intermediate upright beam; andnon-detachably attaching said intermediate upright beam to saidintermediate frame members of said frame portion at distal ends thereof.4. The method for manufacturing said vehicle door assembly as defined inclaim 3, wherein said first steel material of said side frame members isdifferent from said third steel material of said intermediate uprightbeam.
 5. The method for manufacturing said vehicle door assembly definedin claim 4, wherein said second steel material of said intermediateframe members is thicker than said first steel material of said sideframe members and thicker than said third steel material of saidintermediate upright beam.
 6. The method for manufacturing said vehicledoor assembly as defined in claim 4, further comprising the steps of:providing a flat sheet of steel blank of a fourth steel material that isdifferent from said second steel material of said intermediate framemembers; stamping said flat sheet of steel blank into a single gussetbeam; and non-detachably attaching said gusset beam to said frontU-shaped side frame member and said upper intermediate frame member atdistal ends thereof.
 7. The method for manufacturing said vehicle doorassembly as defined in claim 6, wherein said first steel material ofsaid side frame members is different from said fourth steel material ofsaid gusset beam.
 8. The method for manufacturing said vehicle doorassembly as defined in claim 6, wherein said third steel material ofsaid intermediate upright beam is the same as said fourth steel materialof said gusset beam.
 9. The method for manufacturing said vehicle doorassembly as defined in claim 6, wherein said second steel material ofsaid intermediate frame members is thicker than said first steelmaterial of said side frame members, thicker than said third steelmaterial of said intermediate upright beam and thicker than said fourthsteel material of said gusset beam.
 10. The method for manufacturingsaid vehicle door assembly as defined in claim 1, further comprising thesteps of: providing an outer door panel; and attaching said outer doorpanel to said inner panel.
 11. The method for manufacturing said vehicledoor assembly as defined in claim 10, further comprising the steps of:providing a module extension; and attaching said module extension tosaid inner panel so that said inner panel is disposed between said outerdoor panel and said module extension.
 12. The method for manufacturingsaid vehicle door assembly as defined in claim 11, further comprisingthe steps of: providing a window pane; retractably mounting said windowpane between said module extension and said inner panel.
 13. The methodfor manufacturing said vehicle door assembly as defined in claim 1,further comprising the steps of: forming a single outer window framemember and a single inner window frame member; fixing said outer windowframe member and said inner window frame member to each other so as toform a window frame; and attaching said window frame to said innerpanel.
 14. The method for manufacturing said vehicle door assembly asdefined in claim 13, wherein the step of forming said window framecomprises the steps of: providing first, second and third flat sheetsmade of first, second and third outer window steel materials,respectively; non-detachably attaching said first, second and third flatsheets to each other so as to form a single outer window blank; andstamping said outer window blank into said single outer window framemember; said first, second and third outer window steel materials beingdifferent from each other.
 15. The method for manufacturing said vehicledoor assembly as defined in claim 14, wherein said second outer windowsteel material is thicker than both said first outer window steelmaterial and said third outer window steel material.
 16. The method formanufacturing said vehicle door assembly as defined in claim 14, whereinthe step of forming said window frame comprises the steps of: providingfirst and second flat sheets made of first and second inner window steelmaterials, respectively; non-detachably attaching said first and secondflat sheets to each other so as to form a single inner window blank; andstamping said inner window blank into said single inner window framemember; said first and second inner window steel materials beingdifferent from each other.
 17. The method for manufacturing said vehicledoor assembly as defined in claim 16, wherein said second inner windowsteel material is thicker than said first inner window steel material.